1. Field of the Invention
The present invention is broadly concerned with novel, resin compositions and methods of using the same to form non-covalently crosslinked compositions useful in forming gap fill materials, etch mask compositions, spin-on carbon compositions, and anti-reflective coating compositions for lithography processes that are soluble in aqueous alkaline developers.
2. Description of the Prior Art
1. Fill Compositions
Integrated circuit manufacturers are consistently seeking to maximize substrate wafer sizes and minimize device feature dimensions in order to improve yield, reduce unit case, and increase on-chip computing power. As integrated circuit devices grow smaller, there is an increasing need for multi-level interconnects of smaller size and improved feature integrity. The damascene integration scheme is one way to allow for increasing chip densities on a substrate as design rules continue to shrink integrated circuit devices. The damascene process eliminates the need to etch the metal layer that provides the interconnections, permits more densely spaced interconnects, and eliminates the need for dielectric gap-fill materials.
There are two general classes of damascene processes: single damascene and dual damascene. The single damascene process fabricates interconnections by forming a conducting plug through a dielectric layer to connect to the underlying conducting layer. Another dielectric layer is then formed, with the actual interconnect wiring metallization being patterned in the second layer. The dual damascene process constructs multi-level interconnects of smaller size than the single damascene process. The via and trench patterns are patterned into a single dielectric layer and then filled in one step with a conducting material such as a metal. Dual damascene processes involve fewer steps, resulting in smaller, more complex integrated circuit devices, thus lowering manufacturing complexity and cost.
Despite the advantages of dual damascene processes, patterning and etch processes are made more difficult because of feature topography and more complex stack layers. Several techniques have been developed to address such problems, including self-aligned dual damascene, trench-first dual damascene, and via-first dual damascene processes. The application of self-aligned dual damascene is limited, because it requires a thick, intermediate layer to act as an anti-reflective layer, nearly perfect trench and via alignment, and very high etch selectivity between the dielectric and etch-stop layers. Trench-first dual damascene processes involve first masking and etching the trench, and then aligning the via pattern with the newly etched trenches. Successful trench-first dual damascene processes require achieving very uniform trenches and maintaining critical dimension control of vias, which in turn requires high etch selectivity between the dielectric and etch-stop layers. The use of etch-stop layers may also increase the dielectric constant of the dielectric material, possibly leading to device failure.
Via-first dual damascene is a somewhat simpler technique, because the vias are formed on top of the full stack of layers. The vias are etched, followed by lithography processes to form the trench patterns. Via-first dual damascene requires a fill composition capable of protecting the bottom of the via during the trench etch step, and of planarizing the surface to allow easier trench patterning. An organic material is typically used to partially or completely fill the via or contact holes and to protect the bottom and sidewalls from further etch attack during trench etching. In partial fill processes, the gap fill material protects only the bottoms of the via holes, requiring consistent coverage and depth control. In full-fill processes, the vias are completely filled and the layer is planarized. These organic fill materials can also serve as a bottom anti-reflective coating (as discussed below) to reduce or eliminate pattern degradation and line width variation in the patterning of the trench layer, provided the fill material covers the surface of the dielectric layer. After the fill processes, the etching process is performed on the top layer.
Once the structures are filled with gap fill material, the material is then coated with an organic anti-reflective coating layer- and then a photoresist layer. The photoresist is imaged and then the pattern is then transferred down into the substrate using reactive ion etch. In this process, there is almost always residual gap fill material remaining in the structure (via or trench) in the dielectric layer that needs to be removed. This also occurs in trilayer processes where the substrate is coated with a spin-on carbon material that also fills the vias and trenches, instead of a gap fill material. The spin-on carbon layer is then coated with an inorganic hardmask layer, and then a photoresist layer.
The conventional method of removal of the gap fill or spin-on carbon material from the vias and trenches has been to use a high powered oxygen plasma, called an ash process, which essentially burns away the material. This technique was suitable for older technology; however, as the industry moves toward lower k dielectrics, potential problems arise. For example, these low-k dielectrics are usually organic, instead of inorganic, and some are porous. Thus, these new dielectric materials are very susceptible to etch damage, especially from the oxygen ash process. One concern is that the conventional clean-out techniques can cause an increase in the dielectric constant of the material, which negates the purpose of a low-k dielectric to begin with.
2. Anti-Reflective Coatings
During photoresist patterning steps, it is necessary to control reflections from underlying materials through use of an anti-reflective coating to prevent distortion of the photoresist pattern. If the gap-fill material has suitable light-absorbing properties, it can also serve as the anti-reflective layer. Alternatively, an anti-reflective layer can be applied over the gap-fill material before applying the photoresist. While anti-reflective coatings are effective at preventing or minimizing reflection, their use requires an additional break-through step in the process in order to remove the coatings. This necessarily results in an increased process cost.
One solution to this problem has been the use of wet developable anti-reflective coatings. These types of coating can be removed along with the exposed areas of the photoresist material. That is, after the photoresist layer is exposed to light through a patterned mask, the exposed areas of the photoresist are wet developable and are subsequently removed with an aqueous developer to leave behind the desired trench and hole pattern. Wet-developable bottom anti-reflective coatings have typically utilized a polyamic acid soluble in alkaline media as a polymer binder, thus allowing the bottom anti-reflective coating to be removed when the resist is developed. These traditional wet-developable bottom anti-reflective coatings are rendered insoluble in resist solvents taking advantage of a thermally driven amic acid-to-imide conversion. This process works well, however, it has two limitations: (1) the bake temperature window where the bottom anti-reflective coating remains insoluble in organic solvents but soluble in alkaline developer can be narrow (less than 10° C.) due to the covalent crosslinking in the cured layer; and (2) the wet-develop process is isotropic, meaning the bottom anti-reflective coating is removed vertically at the same rate as horizontally, which leads to undercutting of the resist lines. While this is not a problem with larger geometries (greater than 0.2 micron), it can easily lead to line lifting and line collapse at smaller line sizes.
Thus, there is a need for gap fill materials, etch mask compositions, spin-on carbon compositions, and anti-reflective coating compositions, which are removed by conventional photoresist developers while simultaneously exhibiting good coating and optical properties. Control of the rate in which the wet-developable coating dissolves in the developer is also an important factor, and wide bake windows are favorable. There is also a need for gap fill and spin-on carbon materials and methods of removing these materials from vias and trenches that avoids the problems of conventional clean-out methods.